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The Purification of an Inherited Tumor-inducing Factor in Drosophila melanogaster^*

( Division of Biology, California Institute of Technology, Pasadena, California)

1. A semiquantitative assay has been devised for the determination of the tumor-inducing factor (TIF) obtained from larvae of the tu-e mutant of Drosophila melanogaster.

2. The active tumor-inducing factor, which apparently contains protein, was purified 12,000-fold by protein fractionation procedures.

3. The purification process removed substances which inactivate or modify the activity of the tumor-inducing factor in crude or semipurified preparations.

4. Owing to the striking differences in the character of tumors induced by the tumor-inducing factor in crude (free-floating tumors) and purified (invasive and lethal tumors) preparations, the existence of a "modifier" of tumor-inducing factor action is strongly suggested.

^* This work was supported by fellowships from the National Institutes of Health, National Cancer Institute, USPHS CF5154 and CF5155.

Received 5/17/56.